Several types of covers to protect submarine pipelines have been devised. U. K. Pat. No. 1 535 170, for example, discloses a cover with one hinge along its centerline.
To achieve the desired pivot of the cover around one of its two supporting edges and thereby lift of the anchor over the pipeline, if a ship's anchor catches hold of the other edge, a strong reactionary horizontal force against the first-mentioned edge, however, is required.
With only one hinge along the centerline of the cover such strong reaction will occur only in special cases, e.g. when at least two parallel covers are placed close against each other. In the ordinary case the anchor chain will prevent upward movement of the central portion of the cover.